The present invention relates to a compressor, and more particularly, a piston type compressor that can prevent the rotation of the piston.
In a compressor to be used in an air conditioner for a vehicle, the following piston type compressor is known. The structure is a piston, connected to a cam plate operatively connected to a drive shaft, reciprocates in a cylinder bore to perform the compressive operation (for example, Japanese Unexamined Patent Publication No. 11-201037).
That is, in the above-described structure, the drive shaft is rotatably supported in a housing, and a swash plate as the cam plate is operatively connected to the drive shaft to rotate integrally. A cylinder bore is formed in the housing, and a head of a single-headed piston is inserted into the cylinder bore. A shoe seat is concavely formed in the inside of an arm portion of the piston located in the outside of the cylinder bore, and a shoe is received spherically in the shoe seat. A peripheral portion of the swash plate is slidably sandwiched by a pair of the shoes. Furthermore, the rotation of the swash plate accompanied by the rotation of the drive shaft is converted into the reciprocating movement of the piston via the shoes to perform a compression cycle of drawing, compressing and discharging the refrigerant gas into the cylinder bore.
As described above, connection structure between the piston and the swash plate via the shoes allows rotation of the piston about its own axis. If the rotation amount of the piston is large, the vicinity of the arm portion thereof interferes with the rotating swash plate so that vibration and noise tend to occur. Therefore, there is a case that a rotation preventing portion is formed on the arm portion of the piston so as to have a clearance with inner circumferential surface of the housing. The rotation preventing portion is abutted on the housing side to prevent a rotation of the piston when the piston has rotated by predetermined angle.
The housing is mostly manufactured by casting, and a draft for facilitating the separation from an inner mold used in the casting forming is set in the inner circumferential surface of the housing. The inner circumferential surface does not become parallel to reciprocating direction of the piston by virtue of the draft, and amount of the clearances is different between when the piston is at the top dead center and bottom dead center, respectively. Therefore, the inner circumferential surface has been mechanically processed by cutting, etc. so as to become parallel to the reciprocating direction of the piston.
For example, Japanese Unexamined Patent Publication No. 8-337112 discloses a structure that a cubic lug is formed on the outer circumferential surface of the piston, and a sliding groove that is engaged with the lug to be movable axially is formed on the inner circumferential surface of the housing so that the rotation of the piston can be prevented. In this structure, the lug and the sliding groove are formed by means of flat planning process that accompanies a lot of transfer of tools. Furthermore, the above publication also discloses a structure that a rotation preventing portion having an arc convex surface that has a curvature radius larger than the radius of a piston head is provided on the piston, and a recessed portion having an arc concave surface that has a curvature radius larger than the radius of the piston head is provided in the inner circumferential surface of the housing such that the recessed portion is spaced apart from the arc convex surface by predetermined distance. In this structure, though the portions to be processed are reduced than that of the aforementioned constitution, a mechanical processing should be performed after the casting.
However, the mechanical processing of the housing has low productivity, and has been become a factor that causes a cost up. When the mechanical processing is omitted, the draft of the inner circumferential surface needs to be set to be small, so that the drawing of the inner mold becomes difficult and the yield ratio grows worse, and as a result, the productivity is lowered.
Therefore, in view of the aforementioned problems, the object of the present invention is to provide a piston type compressor having a structure that vibration and noise due to interference between the piston and the cam plate can be suppressed by preventing the rotation of the piston, and at the same time, the productivity thereof is high and cost down can be attained.
To solve the above problem, according to the present invention, there is provided a piston type compressor in which a crank chamber is formed within a housing and a drive shaft is rotatably supported in the housing, a cylinder bore being formed in a cylinder block constructing a part of the housing, a piston being accommodated in the cylinder bore so as to be reciprocally moved, a cam plate being operatively connected to the drive shaft, the piston being operatively connected to the cam plate, the piston reciprocating accompanying with the rotation of the drive shaft so that the drawing and the discharging of refrigerant gas is performed, wherein a rotation preventing portion formed on the piston and a groove extending in the axial direction of the piston is formed on an inner circumferential surface of the crank chamber so that the piston is prevented from rotating about its own axis by abutting the rotation preventing portion on the groove; and wherein the crank chamber is formed using an inner mold removable in the axial direction of the piston, and a draft of the groove is set to be small in the inner circumferential surface of the crank chamber.
According to the present invention, when the piston has rotated about its own axis upon receiving the external force by any reasons, the rotation preventing portion provided on the piston abuts on the groove formed in the inner circumferential surface of the crank chamber, so that the rotation amount of the piston is restricted within the predetermined angle. Thereby, it is possible to prevent the interference between the piston and the cam plate and the like, and suppress vibration and noise due to the interference. Also, the groove in the inner circumferential surface of the crank chamber has a draft set to be smaller than those of other portions, and the portions except for the groove may have a draft set to facilitate mold release. Accordingly, it is possible to reduce the portions having small draft and facilitate the mold release, so that the productivity can be improved.
Furthermore, the present invention has such a feature that the above groove is constituted by a cast-forming surface.
According to the present invention, the groove is just as a casting surface, a mechanical processing for finishing the groove can be omitted, thereby, it is possible to improve productivity. Also, although a surface hardened layer is formed in the groove during the casting process, the surface hardened layer is removed if the mechanical processing is performed, so that it becomes a factor that lowers the strength of the housing. In this invention, it is possible to positively leave the surface hardened layer by omitting the mechanical processing and to contribute to improvement of the strength of the housing.
Furthermore, the present invention has a following feature. The above rotation preventing portions are provided two per each piston and one groove per each rotation preventing portion is formed in the inner circumferential surface of the crank chamber, and a recess is formed between the two rotation preventing portions of the piston to obviate an interference with the inner circumferential surface of the crank chamber.
According to the present invention, it is possible to reduce the weight of the piston since the rotation preventing portion can be miniaturized. Also, it is possible to reduce the mold release resistance and to extend durability of the mold because width of the groove having a draft set to be small can be narrowed.
Furthermore, the present invention has a following feature. The above inner mold is provided with a projection which forms the groove, and the projection is detachably mounted to the inner mold.
According to the present invention, the above groove is formed by the projection of the inner mold used when forming the housing that constitutes the inner circumferential surface. Since the projection has a draft set to be small, the resistance due to friction, etc. becomes large upon the mold release so that the projection deteriorates or wears easily. Therefore, maintenance such as partial repair is required very often. In case where the partial repair was repeated and the improvement is no longer possible by the partial repair, the exchange is needed. In this invention, it is unnecessary to exchange the entire inner mold because the projection is detachably mounted to the inner mold. Accordingly, it is advantageous in terms of the production cost.